Here you're begging the question. Murder is unjustified killing, and by calling something murder before you've even fully determined the truth of the justification, your premises irrationally assume the truth of the matter.
By definition murder is not acceptable. The question is, were Kaczynski's actions "murder," and how well does this argument stand the test of reason.
This is extremely difficult, because morality is in large part determined by education and propaganda. For example, if you took someone from our time and raised him in the civil war south U.S., under that system of education and propaganda, would they see a black man's killing of his slave master because he thought it was the only way to escape as unjustified and therefore murder? This is not to say that the morality of all killing is relative! It is merely to point out that the society in which you live has a great role in determining moral justification. Was Kaczynski justified in his actions? Were the people he killed only moral from the perspective of an evil society that is destroying the earth and enslaving humanity? The answer to these questions lies in the truth value of Kaczynski's reasoning. And in this area there is very very little open and honest debate... precisely because, I think, the ideas are far too dangerous and uncomfortable.